In the prior art, there have been proposed various automatic transmission systems having a multistage gear transmission for, for example, trucks, and Japanese Patent Application Public Disclosure No. 115732/86 discloses a control system which is provided with a switch which can be set according to the load condition of the truck to make the feeling at drive-off of the truck the same between the fully loaded condition and the no-load condition of the truck. Furthermore, Japanese Patent Application Public Disclosure No. 72922/88 (corresponding to British Patent Application Public Disclosure No. 2199628) discloses a control system which provided with a variable resistor which can be set according to the load condition at that time for the same purpose. According to these prior art systems, in the case where the clutch is engaged for starting the truck, the operation speed of the clutch in a semi-engaging zone is determined in accordance with the position of the switch, enabling operation of the switch to eliminate the difference in the feeling of vehicle drive-off between at the fully loaded condition and at the no-load condition.
However, in the prior art system the driver must select the suitable gear shift position of the transmission for the load condition of the truck in addition to the operation of the switch when starting out, so that the operations required for starting the truck become complicated.